The present invention pertains to reversible reciprocating piston machines, and particularly to reversible reciprocating piston compressors.
Reciprocating piston compressors, such as the compressor disclosed in U.S. Pat. No. 5,281,110, which is assigned to the present assignee, the disclosure of which is incorporated herein by reference, are generally of fixed displacement and powered by an rotating driving source which operates in a single direction. Also known in the art are reversible reciprocating piston compressors in which a piston has a first stroke length when driven by a crankshaft rotating in a first, forward direction, and a second stroke length when driven by the crankshaft rotating in a second, reverse direction, through use of an eccentric cam which rotates relative to the crankshaft between stops thereon corresponding to first and second angular cam positions which, in turn, correspond to the first and second stroke lengths. These reversible compressors provide the advantage of having one displacement when the crankshaft is rotated in the forward direction, and another displacement when the crankshaft is rotated in the reverse direction. Typical variable stroke, reversible drive compressors, however, do not provide means for positively maintaining the cam in the angular position corresponding to the greater stroke length during rotation of the crankshaft. If the cam is not continually maintained in this angular position during crankshaft rotation, the reexpansion of gas in the cylinder after the piston reaches top-dead-center (TDC) may force the piston away from its TDC position at such a speed that the cam may rotate relative to the crankshaft, separating the cam and crankshaft stops. The separation of these stops result in their subsequently slamming together as the rotating crankshaft catches up to the cam, causing considerable component stresses, adversely affecting durability, and producing undesirable noise.
U.S. patent application Ser. No. 09/099,013, filed Jun. 17, 1998, now U.S. Pat. No. 5,951,261, which is also assigned to the present assignee, the disclosure of which is also incorporated herein by reference, provides a means of preventing separation of the cam and crankshaft stops by locking the cam to the crankshaft in a particular angular position when the crankshaft rotates in one of two directions. According to that disclosure, under the influence of centrifugal force, a latching member comprising a pin is slidably extended from a radial bore provided in the eccentric crankpin into engagement with a mating bore provided in the cam. While locking the crankshaft and cam together, the latching pin is subjected to substantial shear forces which may lead to partial or complete failure of the pin. A more durable means for locking the cam and crankshaft stops together, to prevent their separation upon the reexpansion of gas in the cylinder after the piston reaches TDC is desirable.